The only reason I even care to make a comment is to keep misinformation from running rampant. Will a 4230 do as much work as 2 R tractors? The answer is yes. Two R tractors might move more weight at a low speed but a 4230 will move half the weight twice as fast.
You mentioned that Torque and Horsepower were different terms and I'll agree that they are but they are functions of each other. Without the movement (horsepower) the torsion (torque) is simply dead weight and is not capable of any work. Things have to move to be able to perform work.
You proved your own point by saying " You can have 10,000 ft-lb of torque at zero rpm, holding up a weight. But that is zero hp because nothing is moving". If nothing is moving there is no work getting done. Tractors have to move to pull a plow.
Will a compact utility tractor rated at 50 HP do as much work as an R? Obviously it cant keep up with the R if it was unballasted with the moldboard plow attatched because it would have to pull 1/3 of the load at 3 times the speed which would cause issues with the plow being pulled at 10 MPH. It will however, do just as much work on the PTO as the R and could pull the same plow at the same speed if a guy had enough ballast to weight it down to get traction.
Yes, R tractors are neat and sound really cool but their "cool factor" does mean that they can do more work than their rated horsepower. They can only output 48 HP on the flywheel.
Horsepower is a real nuts and bolts kind of thing, meaning that there is no gray area. A horsepower rating compared to a horsepower rating is like comparing oranges to oranges. It's a scientific measurement of how much work an engine is capable of completing in a given amount of time.
Just an FYI if the R engine spun as fast as the 4230 engine it would make half the torque of the 4230 which is why it has half the HP of the 4230 and is why it pulls the same load at half the speed, or half the load at the same speed.